Development of Antagonists for M5 Muscarinic Acetylcholine Receptor

Drug abuse continues to cause great societal burden. Despite intensive efforts, effective pharmacotherapeutic treatments for drug dependence are still lacking, indicating new strategies and targets are needed. A growing body of evidence supports our hypothesis that selective antagonism at the M5 muscarinic acetylcholine receptor (mAChR) represents a novel target for the treatment of drug dependence. The rewarding effects of most drugs of abuse are believed to be mediated by the mesolimbic dopaminergic pathway projecting from the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) to the nucleus accumbens (NAc) and striatum, respectively. The M5 receptor is the only subtype localized on dopaminergic neurons of the VTA and SNc. Microinfusion of the non-selective mAChR antagonist scopolamine into the VTA or SNc substantially reduces DA release in NAc or striatum, respectively. Although there are no selective M5 receptor antagonists currently available, behavioral studies using mice lacking functional M5 receptors have shown a reduction in reward and withdrawal responses following morphine and cocaine administration, and also a reduction in the rate of cocaine self-administration. These results show a role of the M5 receptor in modulating cocaine and opiate addiction. Furthermore, co-administration of scopolamine with cocaine reduces self-administration of cocaine by rhesus monkeys, and scopolamine has been shown to be effective for detoxification of heroin addicts in clinical studies. We reasoned that the effectiveness of scopolamine is due to antagonism of the M5 receptor; however, the involvement of other subtypes can not be ruled out. To date, the physiological and pharmacological roles of the M5 mAChR are still obscure and research has been hampered by the lack of subtype-selective M5 ligands. The objective of this application is to discover potent and selective M5 receptor antagonists, which, in our long-term goal, can be developed into medical treatments for drug dependence. We expect that compounds developed in this research project will also serve as pharmacological tools useful for studying physiological functions of the M5 receptor. New compounds will be designed and synthesized based on the structural scaffold of literature reports on low selectivity and low potency M5 antagonists. Compounds synthesized will be characterized for receptor binding affinities in recombinant Chinese hamster ovarian (CHO- K1) cells expressing the individual human muscarinic receptor subtypes, ability to inhibit carbachol-induced phosphatidylinositol (P1) hydrolysis in CHO cells expressing hM5 receptors and by inhibition of oxotremorine- evoked dopamine release from superfused rat striatal slices (functional assay).